Your boiler is having trouble 'talking' to your solar panels or an additional heating control part, which might prevent those specific systems from working correctly.

Communication fault: Solar control module or extension module

What causes this fault?

This fault occurs when the boiler's main computer loses its digital connection with the supplementary units that manage your solar thermal panels or extra heating zones. It is usually caused by a loose wiring connection or an internal electronic failure within the expansion module itself, meaning the boiler can no longer send or receive instructions from those parts of your system.